The sensing head of a measuring machine is that part of the machine that contains the work-contacting probe pin, the latter being deflectable in the sensing process; the sensing head also includes a support which reproduces the at-rest position of said sensing pin with a high degree of precision, as well as (a) the measuring systems for the detection and/or measurement of the deflection of the probe pin, and (b) a number of other precision parts which are necessary for operation. It is therefore desirable to protect the sensing head, which is mounted in an exposed position on the measurement arm of the machine, against collision, such as collision with a workpiece which is to be measured. However, it is not easy to provide such protection since contact between the probe pin and the workpiece must, after all, be permitted.
Therefore, as a rule, one merely protects the most sensitive part of the sensing head, namely, the probe pin, from such excessive forces such as may occur in the event of a collision.
Thus, it is known from West German U No. 7,400,071 to fasten the probe pin to the sensing head by means of permanent magnets. Upon a collision, the probe pin drops off and must then be reassembled to the sensing head by hand. This solution is unsatisfactory since it does not even provide sufficient protection for the probe pin itself, which could be damaged by falling off.
West German A No. 1,909,436, describes a protection device for a copying probe. In that case, the sensor housing itself is pulled elastically by a tension spring against detent elements in the form of a three-point support; the sensor housing can therefore yield in the event of a collision. This known device has the disadvantage that the force of the spring which preloads the sensor housing acts perpendicular to the weight of the sensor housing. If a dependable, well-centered seating of the sensor housing is to be obtained, additional means would therefore have to be provided in order to support the sensor housing, or the spring must have a relatively high tensile force. However, such a requirement is inconsistent with the need for easy yieldability in the event of a collision. Furthermore, the sensor returns automatically into the three-point support used only in the case of relatively small deflections. If larger deflections occur, as can happen, for instance, in the event of a collision upon a fast traverse of the machine, the sensor housing would have to be returned manually into its at-rest position.